In view of the continuous trend of technology of increasing the capacity of hard disk devices, the magnetic recording medium of perpendicular recording type is rated as the most promising high density magnetic recording technology of the next generation. Thus, intensive research and development have been carried out actively in recent years with regard to such a magnetic recording medium of perpendicular recording type.
The magnetic recording medium of perpendicular recording type can be classified into two types, the one being a magnetic recording medium of single-layer type having a single magnetic layer for the magnetic recording layer, another being a magnetic recording medium of two-layer type having a backing layer in addition to the magnetic recording layer. The backing layer works as an assist layer at the time of writing information.
In this two-layer type magnetic recording medium, the backing layer is disposed so as to back the magnetic recording layer from below. Because of the predetermined magnetization of the backing layer, the recording magnetic field in the perpendicular direction is increased at the time of recording, and ideal perpendicular recording becomes possible. For this reason, special attention has been paid to the two-layer type magnetic recording medium as the magnetic recording medium suited for the high density recording.
In order to achieve high density magnetic recording, it is very important to reduce the noise. On the other hand, it should be noted that the backing layer of the foregoing two-layer type magnetic recording medium is generally formed with a ferromagnetic material such as FeTaC, NiFe, and the like. When such ferromagnetic material is used for the backing layer, there arises a problem in that noise larger than the noise originating from the magnetic recording layer is caused by the backing layer.
Thereupon, improvements have been made conventionally on the material, and the like, so as to reduce the noise originating from the backing layer. However, a backing layer is required to have a predetermined magnetization in order that the backing layer performs its function. As long as the backing layer has its own magnetization like this, it is difficult to completely remove the noise originating from the backing layer. Further, there has been no satisfactory proposal so far for reducing the noise securely.
As noted before, the original role of the backing layer provided underneath the magnetic recording layer in the two-layer type magnetic recording medium is to assist the recording (writing) of the magnetic information, and for this purpose, it is necessary that the backing layer has a predetermined magnetization. However, such a construction causes the problem of forming noise (spike noise, and the like) originating from the backing layer at the time of reproducing (reading) magnetic information from the magnetic recording layer.
Thus, the backing layer provided to assist the magnetic recording layer is required to satisfy conflicting requirements imposed at the time of recording and imposed at the time of reproducing. Conventionally, there has been no magnetic recording medium of two-layer type capable of satisfying these requirements.
Therefore, the main object of the present invention is to provide a magnetic recording medium of two-layer type comprising a magnetic recording layer and a backing layer assisting recording into the magnetic recording layer, wherein it is possible to suppress the noise originating from the backing layer at the time of reproducing. Further, the present invention has an object of providing a magnetic storage apparatus enabling recording of large-capacity magnetic information by using such a magnetic recording medium.